Bell,T. 1843. The zoology of the voyage of H.M.S. Beagle, under the command of Captain Fitzroy, R.N. during the years 1832 to 1836. Edited and superintended by Charles Darwin ... naturalist to the expedition. Part 5. Reptiles. London, Smith, Elder and Co., (1842-1843), vi + 51 pp. - get paper here